1. Field of the Invention
This invention relates to a liquid crystal material as a display material employed utilizing an electrooptical effect. More particularly, it relates to a ferroelectric liquid crystal mixture and a light-switching element using the same.
2. Description of the Related Art
Ferroelectric liquid crystals are materials capable of realizing an incommensurably quick electrooptical response as compared with that of nematic liquid crystals now broadly used as a display material; thus research in the practical use of the ferroelectric liquid crystals has been made. Among chiral smectic liquid crystal phases known to exhibit ferroelectricity, the chiral smectic C phase (hereinafter abbreviated to SC* phase) has been particularly noted.
The display using the chiral smectic C liquid crystal exhibits
(1) a quicker electrooptical response than that of a nematic liquid crystal, PA1 (2) memory properties and PA1 (3) a wide viewing angle; PA1 (1) exhibition of the SC* phase within a broad temperature range including room temperature, PA1 (2) quick electrooptical response, and PA1 (3) superior alignment. PA1 (1) A ferroelectric smectic C liquid crystal composition comprising the following three components A, B and C, the mixing proportions of component A, component B and component C being 55 to 91% by weight, 5 to 25% by weight and 4 to 20% by weight, respectively, based upon the total quantity of the three components: PA1 (2) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component A is at least one compound selected from compounds expressed by the formula ##STR16## wherein R.sup.7 and R.sup.8 each represent the same or different, linear or branched alkyl group, alkoxy group or alkanoyloxy group each of 1 to 18 carbon atoms, or PA1 (3) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component B is at least one Compound selected from among optically active compounds expressed by either one of the following three formulas, PA1 (4) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component C is at least one compound selected from among optically active compounds expressed by the formula ##STR19## wherein R.sup.17 and R.sup.18 each independently represent a linear or branched alkyl group or alkoxy group each of 1 to 18 carbon atoms and the symbol * represents an asymmetric carbon atom, the above-mentioned optically active compounds having the same sense of the spontaneous polarization in a chiral smectic C phase induced when dissolved in smectic C liquid crystal, as the sense of the compound of the component B. PA1 (5) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component A is at least one compound selected from among compounds expressed by the formula ##STR20## wherein R.sup.7 represents a linear alkyl group, alkoxy group or alkanoyloxy group each of 5 to 14 carbon atoms and R.sup.8 represents a linear alkyl group or alkoxy group each of 4 to 16 carbon atoms, or the formula ##STR21## wherein R.sup.9 and R.sup.10 each independently represent a linear alkyl group or alkoxy group each of 5 to 10 carbon atoms, and having a smectic C phase. PA1 (6) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component A is at least one compound selected from among compounds expressed by the formula ##STR22## wherein R.sup.7 represents a linear alkyl group or alkoxy group each of 6 to 12 carbon atoms and R.sup.8 represents a linear alkoxy group of 6 to 15 carbon atoms, or the formula ##STR23## wherein R.sup.9 represents a linear alkyl group or alkoxy group each of 5 to 8 carbon atoms and R.sup.10 represents a linear alkyl group of 6 to 8 carbon atoms, and having a smectic C phase. PA1 (7) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component A is at least one compound selected from among compounds expressed by the formula ##STR24## wherein R.sup.7 represents an alkyl group of 7 to 14 carbon atoms and R.sup.8 represents an alkyl group of 10 to 14 carbon atoms, or the formula ##STR25## wherein R.sup.9 represents a linear alkyl group or alkoxy group each of 5 to 8 carbon atoms and R.sup.10 represents a linear alkyl group of 6 to 8 carbon atoms, and having a smectic C phase. PA1 (8) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component B is at least one compound selected from among optically active compounds expressed by either one of the following three formulas, PA1 (9) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component C is at least one compound selected from among compounds expressed by the formula ##STR27## wherein R.sup.17 represents a linear alkoxy group of 3 to 10 carbon atoms, R.sup.18 represents an alkyl group of 2 to 6 carbon atoms and the symbol * represents an asymmetric carbon atom, the above-mentioned optically active compounds having the same sense of the spontaneous polarization in a chiral smectic C phase induced when dissolved in smectic C liquid crystal, as the sense of the compound of the component B. PA1 (10) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component A is a smectic C liquid crystal mixture consisting of PA1 (11) A ferroelectric smectic C liquid crystal composition according to item (1), wherein the component B is a compound expressed by the formula ##STR28## and the component C is a compound expressed by the formula ##STR29## (12) A light-switching element containing a ferroelectric smectic C liquid crystal composition as set forth in any one of the above items (1) to (11). PA1 (a) a smectic C liquid crystal mixture comprising at least two components having the smectic C phase, at least one of which is expressed by the formula ##STR36## wherein R.sup.7 represents an alkyl group of 7 to 14 carbon atoms and R.sup.8 represents an alkyl group of 10 to 14 carbon atoms, and having the smectic C phase, and PA1 (b) a smectic C liquid crystal mixture comprising at least two components having the smectic C phase, one of which is a compound described above in (a) and one of which is a compound expressed by the formula ##STR37## wherein R.sup.9 represents a linear alkyl group of 5 to 8 carbon atoms and R.sup.10 represents a linear alkyl group of 6 to 8 carbon atoms, and having a smectic C phase. PA1 a compound of the formula (B-III) wherein R.sup.11 represents a linear alkyl group or alkoxy group each of 3 to 10 carbon atoms and R.sup.12 represents a linear alkyl group or alkoxy group each of 2 to 10 carbon atoms, PA1 a compound of the formula (B-IV) wherein R.sup.13 represents a linear alkyl group or alkoxy group each of 3 to 10 carbon atoms and R.sup.14 represents a linear alkyl group or alkoxy group each of 2 to 10 carbon atoms, and PA1 a compound of the formula (B-V) wherein R.sup.15 represents a linear alkyl group or alkoxy group each of 3 to 10 carbon atoms and R.sup.16 represents a linear alkyl group or alkoxy group each of 2 to 10 carbon atoms. These compounds are illustrated in the following Tables 4, 5 and 6:
hence it has been expected to use the liquid crystal in practice as a material having a potential high density display. At present, requirements for ferroelectric liquid crystals as a practical display material are as follows:
It has been required for the electrooptical response that the response time be 100 .mu.sec or shorter at an impressed voltage of 5 V/.mu.m. Such response properties have been regarded as necessary for highly-multiplexable liquid crystal display elements provided with 640.times.400 lines or more.
As for the method of aligning ferroelectric liquid crystals, three methods referred to as the shearing method, temperature gradient method and surface treatment method have now been attempted. Among these methods, alignment of liquid crystal molecules according to the surface treatment is most preferred in the aspect of commercial production of liquid crystal display elements. In order to apply the surface treatment method now used for aligning nematic liquid crystals also to ferroelectric smectic C liquid crystals, it has been required that the ferroelectric smectic C liquid crystal materials exhibit two liquid crystal phases of the cholesteric phase (hereinafter abbreviated to N* phase) and the smectic A phase (hereinafter abbreviated to SA phase) besides SC* phase, and also that the liquid crystal materials take a phase transition series starting from isotropic liquid phase (hereinafter abbreviated to Iso phase), via the N* phase and the SA phase to the SC* phase (for example, see Japanese patent application laid-open No. Sho 61-250086). An aligning technique according to the surface treatment method of the ferroelectric smectic C liquid crystals deficient in the N* phase or the SA phase has not yet been established.
Japanese patent application laid-open No. Sho 61-291679 illustrates a ferroelectric liquid crystal mixture consisting of a smectic C liquid crystalline pyrimidine compound and a liquid crystal having a SC* phase. Further, the pamphlet of PCT International laid-open WO 86/06401 alike illustrates a ferroelectric liquid crystal mixture having a component of a smectic C liquid crystalline pyrimidine compound. However, these ferroelectric liquid crystals have a response time as long as 300 to 600 .mu.sec; hence they cannot be regarded as practical.
Japanese patent application laid-open No. Sho 63-301290 illustrates a ferroelectric liquid crystal mixture comprising a smectic C liquid crystalline pyrimidine compound and an optically active compound of the formula (B-V) in Example 5. This mixture has superior response properties, but has no N* phase; hence it has a drawback that alignment according to the surface treatment method is impossible.